1. Field of the Invention
This invention relates to the field of video imaging systems. More particularly, this invention relates to methods and apparatus for coupling an optical lens to the optical sensing area of an imaging system.
2. Art Background
A typical video imaging system is comprised of an optical lens system and an integrated circuit die mounted on a printed circuit board. The integrated circuit die implements the imaging electronics. The optical lens system focuses an image scene onto the imaging array. The imaging array generates imaging signals that indicate the contents of the image scene received by the imaging array. Usually, an external circuit receives the imaging signals from the imaging array and generates the video signals.
Typically, the integrated circuit die is bonded into a chip carrier with an adhesive layer, and the chip carrier is bonded to the printed circuit board with an adhesive layer. A set of signal leads provide electrical coupling between the integrated circuit die and the printed circuit board. The optical lens is usually coupled to an optical lens assembly. The optical lens assembly is typically coupled to a threaded insert of a mounting structure.
However, the adhesive layers between the chip carrier and the printed circuit board, and between the integrated circuit die and the chip carrier usually have variable thickness and flatness. The variable thickness and flatness of the adhesive layers, plus the tolerance of the chip carrier, distorts the spacing between the optical lens and the integrated circuit die, thereby causing substantial manufacturing variation. Moreover, the x-y alignment of the integrated circuit die to the optical lens assembly is subject to similar manufacturing variation.
As a consequence, such a prior video imaging system must be calibrated after manufacture to properly focus an image scene on to the imaging array of the integrated circuit die. Typically, the alignment between the optical lens and the integrated circuit die is calibrated by rotating the optical lens assembly inside the threaded insert.
Unfortunately, the mechanisms required in prior imaging systems to calibrate the optical lens assembly results in bulkier and more expensive imaging systems, and increased manufacturing costs for such systems. Moreover, the additional manufacturing steps required to calibrate the optical lens assembly increases manufacturing costs. In addition, the calibrated optical lens assembly is vulnerable to external forces that can throw the system out of calibration.
As will be described, the present invention is a method and apparatus for coupling an optical lens to the imaging array of an imaging system that eliminates the need to calibrate the optical lens. The method and apparatus enables high volume low-cost automated manufacturing of imaging systems.